Module: Sprockets::SourceMapUtils

Extended by:
SourceMapUtils
Included in:
Base, SourceMapUtils
Defined in:
lib/sprockets/source_map_utils.rb

Constant Summary collapse

VLQ_BASE_SHIFT =

Public: Base64 VLQ encoding

Adopted from ConradIrwin/ruby-source_map

https://github.com/ConradIrwin/ruby-source_map/blob/master/lib/source_map/vlq.rb

Resources

http://en.wikipedia.org/wiki/Variable-length_quantity
https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
https://github.com/mozilla/source-map/blob/master/lib/source-map/base64-vlq.js
5
VLQ_BASE =
1 << VLQ_BASE_SHIFT
VLQ_BASE_MASK =
VLQ_BASE - 1
VLQ_CONTINUATION_BIT =
VLQ_BASE
BASE64_DIGITS =
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('')
BASE64_VALUES =
(0...64).inject({}) { |h, i| h[BASE64_DIGITS[i]] = i; h }

Instance Method Summary collapse

Instance Method Details

#bsearch_mappings(mappings, offset, from = 0, to = mappings.size - 1) ⇒ Object

Public: Search Array of mappings for closest offset.

mappings - Array of mapping Hash objects offset - Array [line, column]

Returns mapping Hash object.


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# File 'lib/sprockets/source_map_utils.rb', line 270

def bsearch_mappings(mappings, offset, from = 0, to = mappings.size - 1)
  mid = (from + to) / 2

  if from > to
    return from < 1 ? nil : mappings[from-1]
  end

  case compare_source_offsets(offset, mappings[mid][:generated])
  when 0
    mappings[mid]
  when -1
    bsearch_mappings(mappings, offset, from, mid - 1)
  when 1
    bsearch_mappings(mappings, offset, mid + 1, to)
  end
end

#combine_source_maps(first, second) ⇒ Object

Public: Combine two seperate source map transformations into a single mapping.

Source transformations may happen in discrete steps producing separate source maps. These steps can be combined into a single mapping back to the source.

For an example, CoffeeScript may transform a file producing a map. Then Uglifier processes the result and produces another map. The CoffeeScript map can be combined with the Uglifier map so the source lines of the minified output can be traced back to the original CoffeeScript file.

Returns a source map hash.


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# File 'lib/sprockets/source_map_utils.rb', line 153

def combine_source_maps(first, second)
  return second unless first

  _first  = decode_source_map(first)
  _second = decode_source_map(second)

  new_mappings = []

  _second[:mappings].each do |m|
    first_line = bsearch_mappings(_first[:mappings], m[:original])
    new_mappings << first_line.merge(generated: m[:generated]) if first_line
  end

  _first[:mappings] = new_mappings

  encode_source_map(_first)
end

#compare_source_offsets(a, b) ⇒ Object

Public: Compare two source map offsets.

Compatible with Array#sort.

a - Array [line, column] b - Array [line, column]

Returns -1 if a < b, 0 if a == b and 1 if a > b.


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# File 'lib/sprockets/source_map_utils.rb', line 251

def compare_source_offsets(a, b)
  diff = a[0] - b[0]
  diff = a[1] - b[1] if diff == 0

  if diff < 0
    -1
  elsif diff > 0
    1
  else
    0
  end
end

#concat_source_maps(a, b) ⇒ Object

Public: Concatenate two source maps.

For an example, if two js scripts are concatenated, the individual source maps for those files can be concatenated to map back to the originals.

Examples

script3 = "#{script1}#{script2}"
map3    = concat_source_maps(map1, map2)

a - Source map hash b - Source map hash

Returns a new source map hash.


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# File 'lib/sprockets/source_map_utils.rb', line 73

def concat_source_maps(a, b)
  return a || b unless a && b
  a, b = make_index_map(a), make_index_map(b)

  if a["sections"].count == 0 || a["sections"].last["map"]["mappings"].empty?
    offset = 0
  else
    offset = a["sections"].last["map"]["mappings"].count(';') + 
             a["sections"].last["offset"]["line"] + 1
  end

  a["sections"] += b["sections"].map do |section|
    {
      "offset" => section["offset"].merge({ "line" => section["offset"]["line"] + offset }),
      "map"    => section["map"].merge({
        "sources" => section["map"]["sources"].map do |source|
          PathUtils.relative_path_from(a["file"], PathUtils.join(File.dirname(b["file"]), source))
        end
      })
    }
  end
  a
end

#decode_source_map(map) ⇒ Object

Public: Decompress source map

Example:

decode_source_map(map)
# => {
  version:  3,
  file:     "..",
  mappings: [
    { source: "..", generated: [0, 0], original: [0, 0], name: ".."}, ..
  ],
  sources:  [..],
  names:    [..]
}

map - Source map hash (v3 spec)

Returns an uncompressed source map hash


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# File 'lib/sprockets/source_map_utils.rb', line 189

def decode_source_map(map)
  return nil unless map

  mappings, sources, names = [], [], []
  if map["sections"]
    map["sections"].each do |s|
      mappings += decode_source_map(s["map"])[:mappings].each do |m|
        m[:generated][0] += s["offset"]["line"]
        m[:generated][1] += s["offset"]["column"]
      end
      sources |= s["map"]["sources"]
      names   |= s["map"]["names"]
    end
  else
    mappings = decode_vlq_mappings(map["mappings"], sources: map["sources"], names: map["names"])
    sources  = map["sources"]
    names    = map["names"]
  end
  {
    version:  3,
    file:     map["file"],
    mappings: mappings,
    sources:  sources,
    names:    names
  }
end

#decode_vlq_mappings(str, sources: [], names: []) ⇒ Object

Public: Decode VLQ mappings and match up sources and symbol names.

str - VLQ string from 'mappings' attribute sources - Array of Strings from 'sources' attribute names - Array of Strings from 'names' attribute

Returns an Array of Mappings.


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# File 'lib/sprockets/source_map_utils.rb', line 294

def decode_vlq_mappings(str, sources: [], names: [])
  mappings = []

  source_id       = 0
  original_line   = 1
  original_column = 0
  name_id         = 0

  vlq_decode_mappings(str).each_with_index do |group, index|
    generated_column = 0
    generated_line   = index + 1

    group.each do |segment|
      generated_column += segment[0]
      generated = [generated_line, generated_column]

      if segment.size >= 4
        source_id        += segment[1]
        original_line    += segment[2]
        original_column  += segment[3]

        source   = sources[source_id]
        original = [original_line, original_column]
      else
        # TODO: Research this case
        next
      end

      if segment[4]
        name_id += segment[4]
        name     = names[name_id]
      end

      mapping = {source: source, generated: generated, original: original}
      mapping[:name] = name if name
      mappings << mapping
    end
  end

  mappings
end

#encode_source_map(map) ⇒ Object

Public: Compress source map

Example:

encode_source_map(map)
# => {
  "version"  => 3,
  "file"     => "..",
  "mappings" => "AAAA;AACA;..;AACA",
  "sources"  => [..],
  "names"    => [..]
}

map - Source map hash (uncompressed)

Returns a compressed source map hash according to source map spec v3


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# File 'lib/sprockets/source_map_utils.rb', line 232

def encode_source_map(map)
  return nil unless map
  {
    "version"  => map[:version],
    "file"     => map[:file],
    "mappings" => encode_vlq_mappings(map[:mappings], sources: map[:sources], names: map[:names]),
    "sources"  => map[:sources],
    "names"    => map[:names]
  }
end

#encode_vlq_mappings(mappings, sources: nil, names: nil) ⇒ Object

Public: Encode mappings Hash into a VLQ encoded String.

mappings - Array of Hash mapping objects sources - Array of String sources (default: mappings source order) names - Array of String names (default: mappings name order)

Returns a VLQ encoded String.


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# File 'lib/sprockets/source_map_utils.rb', line 343

def encode_vlq_mappings(mappings, sources: nil, names: nil)
  sources ||= mappings.map { |m| m[:source] }.uniq.compact
  names   ||= mappings.map { |m| m[:name] }.uniq.compact

  sources_index = Hash[sources.each_with_index.to_a]
  names_index   = Hash[names.each_with_index.to_a]

  source_id     = 0
  source_line   = 1
  source_column = 0
  name_id       = 0

   = mappings.group_by { |m| m[:generated][0] }

  ary = (1..(.keys.max || 1)).map do |line|
    generated_column = 0

    ([line] || []).map do |mapping|
      group = []
      group << mapping[:generated][1] - generated_column
      group << sources_index[mapping[:source]] - source_id
      group << mapping[:original][0] - source_line
      group << mapping[:original][1] - source_column
      group << names_index[mapping[:name]] - name_id if mapping[:name]

      generated_column = mapping[:generated][1]
      source_id        = sources_index[mapping[:source]]
      source_line      = mapping[:original][0]
      source_column    = mapping[:original][1]
      name_id          = names_index[mapping[:name]] if mapping[:name]

      group
    end
  end

  vlq_encode_mappings(ary)
end

#format_source_map(map, input) ⇒ Object

Public: Transpose source maps into a standard format

NOTE: Does not support index maps

version => 3 file => logical path sources => relative from filename

Unnecessary attributes are removed

Example

map
#=> {
#  "version"        => 3,
#  "file"           => "stdin",
#  "sourceRoot"     => "",
#  "sourceContents" => "blah blah blah",
#  "sources"        => [/root/logical/path.js],
#  "names"          => [..],
#}
format_source_map(map, input)
#=> {
#  "version"        => 3,
#  "file"           => "logical/path.js",
#  "sources"        => ["path.js"],
#  "names"          => [..],
#}

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# File 'lib/sprockets/source_map_utils.rb', line 37

def format_source_map(map, input)
  filename      = input[:filename]
  load_path     = input[:load_path]
  load_paths    = input[:environment].config[:paths]
  mime_exts     = input[:environment].config[:mime_exts]
  pipeline_exts = input[:environment].config[:pipeline_exts]
  file          = PathUtils.split_subpath(load_path, filename)
  {
    "version"  => 3,
    "file"     => file,
    "mappings" => map["mappings"],
    "sources"  => map["sources"].map do |source|
      source = URIUtils.split_file_uri(source)[2] if source.start_with? "file://"
      source = PathUtils.join(File.dirname(filename), source) unless PathUtils.absolute_path?(source)
      _, source = PathUtils.paths_split(load_paths, source) 
      source = PathUtils.relative_path_from(file, source)
      PathUtils.set_pipeline(source, mime_exts, pipeline_exts, :source)
    end,
    "names"    => map["names"]
  }
end

#make_index_map(map) ⇒ Object

Public: Converts source map to index map

Example:

map
# => {
  "version"  => 3,
  "file"     => "..",
  "mappings" => "AAAA;AACA;..;AACA",
  "sources"  => [..],
  "names"    => [..]
}
make_index_map(map)
# => {
  "version"  => 3,
  "file"     => "..",
  "sections" => [
    {
      "offset" => { "line" => 0, "column" => 0 },
      "map"    => {
        "version"  => 3,
        "file"     => "..",
        "mappings" => "AAAA;AACA;..;AACA",
        "sources"  => [..],
        "names"    => [..]
      }
    }
  ]
}

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# File 'lib/sprockets/source_map_utils.rb', line 126

def make_index_map(map)
  return map if map.key? "sections"
  {
    "version"  => map["version"],
    "file"     => map["file"],
    "sections" => [
      {
        "offset" => { "line" => 0, "column" => 0 },
        "map"    => map
      }
    ]
  }
end

#vlq_decode(str) ⇒ Object

Public: Decode a VLQ string.

str - VLQ encoded String

Returns an Array of Integers.


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# File 'lib/sprockets/source_map_utils.rb', line 426

def vlq_decode(str)
  result = []
  chars = str.split('')
  while chars.any?
    vlq = 0
    shift = 0
    continuation = true
    while continuation
      char = chars.shift
      raise ArgumentError unless char
      digit = BASE64_VALUES[char]
      continuation = false if (digit & VLQ_CONTINUATION_BIT) == 0
      digit &= VLQ_BASE_MASK
      vlq   += digit << shift
      shift += VLQ_BASE_SHIFT
    end
    result << (vlq & 1 == 1 ? -(vlq >> 1) : vlq >> 1)
  end
  result
end

#vlq_decode_mappings(str) ⇒ Object

Public: Decode a VLQ string into mapping numbers.

str - VLQ encoded String

Returns an two dimensional Array of Integers.


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# File 'lib/sprockets/source_map_utils.rb', line 465

def vlq_decode_mappings(str)
  mappings = []

  str.split(';').each_with_index do |group, index|
    mappings[index] = []
    group.split(',').each do |segment|
      mappings[index] << vlq_decode(segment)
    end
  end

  mappings
end

#vlq_encode(ary) ⇒ Object

Public: Encode a list of numbers into a compact VLQ string.

ary - An Array of Integers

Returns a VLQ String.


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# File 'lib/sprockets/source_map_utils.rb', line 405

def vlq_encode(ary)
  result = []
  ary.each do |n|
    vlq = n < 0 ? ((-n) << 1) + 1 : n << 1
    loop do
      digit  = vlq & VLQ_BASE_MASK
      vlq  >>= VLQ_BASE_SHIFT
      digit |= VLQ_CONTINUATION_BIT if vlq > 0
      result << BASE64_DIGITS[digit]

      break unless vlq > 0
    end
  end
  result.join
end

#vlq_encode_mappings(ary) ⇒ Object

Public: Encode a mapping array into a compact VLQ string.

ary - Two dimensional Array of Integers.

Returns a VLQ encoded String seperated by , and ;.


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# File 'lib/sprockets/source_map_utils.rb', line 452

def vlq_encode_mappings(ary)
  ary.map { |group|
    group.map { |segment|
      vlq_encode(segment)
    }.join(',')
  }.join(';')
end